1. Field of the Invention
The present invention relates to a weft yarn storage unit for use in a shuttleless loom known as a jet loom, rapier and the like.
2. Description of the Prior Art
Shuttleless looms known as jet looms measure and store a length of weft yarn to be inserted each time it is taken through the warp shed for intermittent weft insertion on a jet of fluid such as air or liquid.
One conventional type of weft yarn storage unit for use in jet looms measures and stores weft yarn by winding the latter around the circumference of a yarn storage drum for a predetermined number of convolutions or turns. The stored length of weft yarn is drawn off axially of the yarn storage drum by a jet of fluid ejected from a weft insertion device in order to be placed in the warp shed.
The weft yarn, which is drawn at a high speed by the jet of fluid from the weft insertion device in the axial direction of the yarn storage drum (stationary, i.e. not rotatable) is withdrawn around the outer peripheral surface of the yarn storage drum with its rotation and is subjected to centrifugal forces due to the ballooning phenomenon. The centrifugal forces place the weft yarn under tension, resulting in an obstacle to high-speed weft insertion operation. The weft yarn as thus tensioned needs to be driven under a high pressure of jet of fluid, which tends to cause yarn breakage.
Another proposed yarn storage unit includes a yarn storage drum rotatable about its own axis for drawing weft yarn off a yarn supply package under rotational forces to measure and store a length of weft yarn. With this type of yarn storage unit, resistance to weft insertion operation (i.e. back tension) is slightly smaller than that in other conventional yarn storage units in which the yarn storage drum is fixed in position. However, since the yarn storage drum rotates to unreel the weft yarn from the yarn supply package, the circumferential speed of the yarn storage drum is equal to the speed at which the weft yarn is drawn from the yarn supply package. With the circumferential speed of the yarn storage drum being low, the weft yarn as it is unwound from the yarn storage drum still suffers from ballooning, and it is impossible to reduce back tension to a sufficient degree.
There has heretofore been proposed another device for measuring weft yarn with a feed roller rotatable in synchronism with the rotational frequency of the loom and for storing the measured length of weft yarn in the shape of a U as it floats on an ejected jet of air. The floating weft yarn however is unstable in attitude, and undergoes snarling or has twisted weft yarn lengths, resulting in a tendency to produce defective woven fabrics. For larger cloth widths, this yarn storage device increases back tension imposed on the weft yarn, and hence fails to store the weft yarn stably, effect high-speed yarn ejection and prevent yarn breakage when the warp shed is wider.